A) Field of the Invention
The present invention relates to a semiconductor device and its manufacture method, and more particularly to a semiconductor device having a high dielectric constant gate insulating film and its manufacture method.
B) Description of the Related Art
Insulated gate (IG) type field effect transistors (FET), typically MOS transistors, are widely used as representative semiconductor elements of a semiconductor integrated circuit device. In order to achieve high integration of semiconductor integrated circuit devices, IG-FETs have been miniaturized in accordance with scaling rules. Miniaturization such as thinning a gate insulating film and shortening a gate length reduces each size of IG-FET and can improve the performance of IG-FET while maintaining the performance of each miniaturized element normally.
MOS transistors of the next generation are required to set the gate length to sub 100 nm and thin the gate oxide film to 2 nm or thinner. At this thickness, tunnelling current starts to flow directly so that gate leak current increases and a consumption power increases. There is a limit in miniaturization so long as silicon oxide is used as the material of the gate insulating film. In order to suppress tunneling current flowing through the gate insulating film, it is desired to use a thick gate insulating film.
It has been proposed to use insulating material having a dielectric constant higher than that of silicon oxide as the material of a gate insulating film, in order to increase a physical film thickness while an equivalent oxide film thickness (EOT) is set to 2 nm or thinner. It is said that a relative dielectric constant of silicon oxide is about 3.5 to 4.5 (e.g., 3.9) although it depends on a film forming method. Silicon nitride has a dielectric constant higher than that of silicon oxide and it is said that silicon nitride has a relative dielectric constant of about 7 to 8 (e.g., 7.5).
Japanese Patent Laid-open Publication No. 2001-274378 proposes to use: as the material of a gate insulating film, materials having a dielectric constant higher than that of silicon oxide such as: barium titanic acid (Ba(Sr)TiO3) having a relative dielectric constant of 200 to 300; titanium oxide (TiO2) having a relative dielectric constant of about 60; tantalum oxide (Ta2O5), zirconium oxide (ZrO2), and hafnium oxide (HfO2) having a relative dielectric constant of about 25; silicon nitride (Si3N4) having a relative dielectric constant of about 7.5; and alumina (Al2O3) having a relative dielectric constant of about 7.8. It also proposes the structure that a silicon oxide film is interposed between a high dielectric constant insulating material film of the above-described materials and a silicon substrate.
In this specification, compounds are expressed in some cases in the form of HfO, HfSiON, SiO and the like. These expressions are intended to have not only a chemical stoichiometric composition but also a composition shifted from the chemical stoichiometric composition.
Adopting new materials having a high dielectric constant as the material of a gate insulating film of IG-FET poses a new problem. Namely, zirconium oxide and hafnium oxide are crystallized by a high temperature process so that leak current increases through electric conduction via crystal grain boundaries and defect levels. It is desired to solve this new problem in order to promote practical usage of new materials.
Japanese Patent Laid-open Publication No. 2001-77111 proposes to hinder the formation of crystalline structures and maintain an amorphous phase by adding aluminum oxide to zirconium oxide and hafnium oxide.
Japanese Patent Laid-open Publication No. 2003-8011 proposes to improve thermal stability by adding silicon oxide to hafnium oxide.
Japanese Patent Laid-open Publication No. 2003-23005 indicates that if a high dielectric constant material (high-k material) layer made of metal oxide is formed on a silicon substrate, a silicon oxide layer is formed at the interface between the metal oxide film and silicon substrate, and proposes to flow hydrogen in place of oxygen before the metal oxide film is formed.
Japanese Patent Laid-open Publication No. 2002-359370 proposes to form a nitrogen atom layer on both surfaces of a high dielectric constant gate insulating film in order to suppress impurity diffusion from the gate electrode into a silicon substrate and diffusion of metal elements and oxygen from the gate insulating film into the gate electrode or silicon substrate.
An oxynitride film having Hf as its main composition has a relative dielectric constant several to about ten times higher than that of silicon oxide. It is an urgent issue to develop an oxynitride film capable of being used as the material of a gate insulating film of the sub 100 nm node generation. Polysilicon is anticipated to be used as the material of the gate electrode, and the insulated gate electrode structure is expected to be a structure of polysilicon/high-k insulating film/SiO(N)/silicon substrate.